JP2005101534A - Method to control sequence of measurement steps for aligning a semiconductor wafer in exposure system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a percentage of time used to move a wafer stage during an alignment. <P>SOLUTION: The method to control the sequence of measurement steps for aligning a semiconductor wafer includes steps of: (a) preparing a semiconductor wafer in exposure equipment; (b) starting a first alignment measurement step; (c) selecting the first number of exposure fields to determine the first sequence; (d) moving the semiconductor wafer to an alignment position; (e) storing the alignment position of the exposure field last moved; (f) terminating the first alignment measurement step, starting a second alignment measurement step, selecting the exposure field whose position was stored, further selecting an exposure field to determine a second sequence, and repeating the steps (d) to (f) for the alignment measurement step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for controlling a sequence of measurement steps for aligning a semiconductor wafer in an exposure apparatus, and after the completion of a plurality of alignment measurement steps, the exposure apparatus sequentially exposes the structure pattern of the mask onto the wafer, respectively. On how to do.

  In the manufacture of integrated circuits, a structure pattern to be formed on a wafer is generated in a photosensitive layer provided on a semiconductor wafer by sequentially imaging a structure pattern formed on a mask. Typically, multiple exposure fields, each with the same structural pattern, are provided on the wafer based on the ratio of the size of such mask to the wafer to be exposed and based on the reduced projection of the mask onto the wafer. Is done. Therefore, in the exposure apparatus, stepper or scanner used for this purpose, each exposure field is sequentially transferred onto the wafer.

  Typically, the exposure field is distributed on the wafer surface in a regular array of matrix shapes. If each exposure field protrudes from the wafer edge, at least the circuit projected on the wafer edge will fall off.

  Prior to initiating the first layer level patterning with the mask on the wafer, the matrix of exposure fields is determined. After sequentially exposing the first level, each subsequent level needs to be aligned on a pre-imaged layer level that together produce a circuit together. Wafer alignment is typically performed in a sequence of individual predetermined alignment measurement steps. Each of these alignment measurement steps plays a part in detecting and aligning the current position of the semiconductor wafer including the formed structure with respect to the projection system in the exposure apparatus.

  For each measurement step, a dedicated alignment mark is provided in the individual exposure field as part of the projected structure pattern. These alignment masks correspond in size, form, and alignment to the requirements that arise in the individual alignment measurement steps. Such alignment marks are typically in the area of the saw frame, i.e. the edge region of the exposure field, or, for example, if there are multiple circuits in the exposure field, two integrated circuits to be formed on the wafer. Positioned in the intermediate space.

  For each case, an exposure field on the wafer, typically multiple but not all, may be used to perform one of the alignment measurement steps. Here, in most cases, it is sufficient that 1 to 8 exposure fields distributed on the surface of the wafer are selected and the alignment marks formed thereon are evaluated after measurement to determine the position. is there.

  Once the position has been determined, corrections can be made to the undesired tilt angles that the wafer can take, eg, with respect to the ideal image plane of the projection system, on the movable wafer stage. On the other hand, at a specific position, the coordinate system of the movable wafer stage can be calibrated, so that it can be moved to the correct position when exposing.

  According to the prior art, especially when a larger number of exposure fields are used in the exposure measurement step, the respective sequence in which the exposure fields are used for measurement is determined in an optimal manner. When determining the sequence, it should be noted that the distance between two exposure fields that are used consecutively without interruption of the alignment mark for alignment measurement is made as small as possible. For example, in order to perform individual measurements mainly in the exposure field located in the edge region of the wafer, the group of exposure fields is moved in a circle. The advantage is that this eliminates the long distance movement of the wafer stage, which significantly reduces the non-productive preparation time used only for alignment.

  It is an object of the present invention to obtain further time advantages by further reducing the proportion of time used to move the wafer stage during alignment relative to the total duration that the wafer occupies the exposure apparatus. It is.

  This object is achieved by a method for controlling a sequence of measurement steps for aligning a semiconductor wafer in an exposure apparatus, wherein the semiconductor wafer has a regular array of exposure fields, the method comprising (a ) Preparing a semiconductor wafer in the exposure apparatus; (b) starting a first alignment measurement step; and (c) selecting an initial number of exposure fields and determining a first sequence. Wherein for each case, the number of selected exposure fields is used to perform at least one measurement, and d) movable to move each of the selected exposure fields Using the wafer stage, move the semiconductor wafer to the alignment position with respect to the alignment optical element of the exposure tool. E) a step of storing the alignment position of the exposure field that has been moved last, f1) a step of ending the first alignment measurement step, and f2) a second alignment measurement step immediately following. G) selecting an exposure field whose position is stored to perform a first measurement in a second sequence of exposure fields in the exposure field; and h) selecting an additional number of exposure fields. And determining a second sequence, wherein the number of further selected exposure fields is utilized to perform at least one further measurement, respectively, after the first measurement in the sequence. Steps d) to f1) for the alignment measurement step immediately following i) Including the step of repeating.

  This object is achieved by a method in which an exposure apparatus sequentially exposes a mask structure pattern onto a wafer after a plurality of alignment measurement steps, respectively, wherein the wafer has a regular array of exposure fields. And the exposure field on the wafer to be exposed first in the sequence of exposures is the exposure field used to perform the measurement as the last exposure field in the alignment measurement performed immediately before the exposure step. It is characterized by being identical.

  In the sequence of the alignment measurement step, after the end of the alignment measurement step, the present invention carries the exposure field different from the last measured to the region of the alignment optical element that measures the alignment mark in the exposure field. The fact that the wafer stage does not need to be moved is based on the idea that the time for the wafer to occupy the exposure apparatus can be further saved.

  Therefore, according to the present invention, when selecting an exposure field in the alignment measurement step that immediately follows and when determining the sequence of exposure fields to be measured continuously, the last measured exposure field is new. Note that it is used as the exposure field to be measured first in the measurement step. In this case, the new measurement step need not have a causal relationship with the previous step. It is not necessary to measure the same alignment mark in the same exposure field in both of these partial steps. What is critical is that within the exposure field, the exposure field is not moved relative to the alignment optics, or the wafer stage is moved by a magnitude ratio distance.

  The alignment optical element may be a lens system provided separately from the projection lens system with respect to the wafer stage inside the exposure apparatus, and includes a detector, a control unit, and an illuminator. The element can also be an alignment optical element that uses a lens system of a projection optical element. For example, a beam incident from an alignment mark in an exposure field is separated by a beam splitter.

  The selection of groups of exposure fields and, further, the determination of the sequence is grouped, i.e. the selection of exposure fields when performing individual measurements in a previously performed alignment measurement step, and the sequence of these fields. Will be executed accordingly. In general, the complete alignment sequence, ie the entire alignment measurement step with all individual measurements in the exposure field, is predetermined in the control sequence of the exposure unit. Thus, the present invention first selects and determines the sequence and grouping or number of exposure fields for a later or final alignment measurement step, and then only controls the prior alignment measurement step. Including the case of adapting sequentially.

  Here, the alignment measurement step is understood to be a closed sequence of measurements in a plurality of exposure fields, where the partial alignment or orientation determination of the wafer relative to the projection apparatus, in particular the alignment optics related system. An aspect is determined. One example of the alignment measurement step of the present invention is a preliminary alignment that is performed as a first step after a purely mechanical alignment, typically using notches often provided in semiconductor wafers.

  A further example relates to so-called tilt measurement, i.e. measurement of the tilt angle and orientation of the tilt of the wafer on the stage relative to the ideal image plane of the alignment optics or projection system. A further important alignment step relates to fine alignment, which can be further divided into sub-steps.

  The invention particularly relates to an alignment measurement step to be performed comprehensively on the wafer. In particular, in this case, the exposure field is moved continuously for a particular partial aspect of the alignment in order to inspect subsequent partial aspects after the determination of the partial aspect by a series of measurements.

  Thus, the present invention is not very applicable when, for example, field-specific alignment measurement steps are performed between individual sequential exposures (this is especially true for the determination of focus values). However, the focus setting can basically also be determined in a comprehensive step before exposure by measuring a plurality of exposure fields, so that the method according to the invention can be applied here as well.

  The method according to the invention is a method for controlling the sequence of measurement steps for aligning a semiconductor wafer (10) in an exposure apparatus, the semiconductor wafer having a regular array of exposure fields (12), a) preparing the semiconductor wafer (10) in the exposure apparatus; b) initiating a first alignment measurement step; c) selecting an initial number of exposure fields (16); and Determining a sequence of numbers (No. 1, No. 2), wherein for each case, the number of selected exposure fields (16) is used to perform at least one measurement; and D) using a movable wafer stage to move each of the selected exposure fields (16, 1, 2), the semiconductor wafer (1 ) To the alignment position with respect to the alignment optical element of the exposure apparatus, e) storing the alignment position of the exposure field (16, 2) last moved, and f1) the first alignment. Ending the measurement step; f2) starting the second alignment measurement step immediately following; g) performing the first measurement in the second sequence of exposure fields in the exposure field; Selecting the exposure field (16 ′, number 1) in which the position is stored; and h) selecting a further number of exposure fields (16 ′) and the second sequence (numbers 2 to 8). Performing at least one further measurement in the sequence after the first measurement, respectively, after the first measurement The number of the further selected exposure fields (16 ′, # 2-8) is utilized, and i) repeating the steps d) to f1) for the alignment measurement step that immediately follows. Thus, the above object is achieved.

  Said first and / or said second alignment measuring steps each determine a first coarse alignment of said wafer in an image plane of said exposure apparatus, an inclination of said wafer (10) relative to said image plane; It may be characterized in that it includes elements of the group consisting of fine alignment of the wafer (10) in the image plane.

  The steps d) to f1) may be repeated for all alignment measurement steps before the exposure of the semiconductor wafer (10).

  The method of the present invention is a method in which, after completing a plurality of alignment steps, in an exposure apparatus, wafers each having a mask structure pattern are sequentially exposed, wherein the wafer (10) has a regular array of exposure fields ( The exposure field (No. 12, No. 1) to be exposed first on the wafer in the exposure sequence (No. 1 to No. 56) is performed immediately before the exposure step. In the alignment measurement step, it is characterized in that it is identical to the exposure field (16) used as the last exposure field (16, 6) in order to carry out the measurement, whereby the above object is achieved.

  The alignment step performed immediately before the exposure step is a fine alignment step of the semiconductor wafer on the image plane of the exposure apparatus, whereby the above object is achieved.

  The invention will now be described in more detail with reference to exemplary embodiments and using the drawings.

  A regular arrangement of the matrix shape of the exposure field 12 is shown in FIG. 1 in a top view of each of the wafers 10 having a diameter of 200 mm and in a sequence of exemplary method steps for alignment. Accurate positioning of the array on the wafer is usually done in an optimized manner that ensures that the largest possible number of placeable exposure fields or circuits / chips are placed on the wafer surface of the product.

  The exemplary embodiment shown in FIG. 1 corresponds to a conventionally applied method for controlling the alignment measurement step. Canon FPA 5000-ES2 + can now be used as the exposure apparatus. In the above-mentioned plane, in the structure pattern already projected onto the exposure field, suitable apparatus-specific alignment marks have already been incorporated into the design.

  Those skilled in the art of lithographic projection will appreciate that the methods described herein are equally applicable to exposure equipment from other manufacturers, in particular, from Nikon or ASML, and that multiple methods may be used on the wafer. It is clear that 300 mm wafers or larger diameter wafers can also be used if there is room for more exposure fields.

  In this example, there is room for 56 exposure fields, at least partially on the wafer. In order to determine the individual exposure fields, numbers are given for each row and column in the drawing.

  The first alignment step (not shown) without actual measurement is the mechanical mounting of the wafer 10 on the wafer stage, where the notches at the wafer edge collide with corresponding devices on the wafer stage; This allows the wafer to still be very rough, first simply mechanically pre-aligned.

  A first alignment measurement step is shown in FIG. 1A. The two exposure fields selected for this measurement step are marked by applying a dark shade to the exposure field which is generally shown in light colour. The measurement steps are shown as pre- or coarse alignments (but can be distinguished from mechanical alignments, as compared to this mechanical alignment, these alignments already give much more accurate results) Alignment, TVPA).

  In order to calibrate the coordinates of the wafer stage in the XY image plane of the projection optics, the alignment mark is inspected during this alignment measurement step and a known position is used in the design. The exposure field 14 selected here for measurement is selected using a criterion that can be positioned such that the exposure fields are spaced from each other and not in close proximity to the edge of the wafer. The sequence of individual measurements is arbitrary.

  FIG. 1B shows a further second alignment measurement step (GTILT) according to the first alignment measurement step and carried out only for example for the first wafer 10 in a batch comprising 25 substantially identical wafers. , Global tilt). For all further wafers, the subsequent steps correspond to the example shown in FIG. 1E, which is further described below and indicates fine alignment.

  The second alignment measurement step is here represented by so-called tilt measurement. For example, a laser is used to illuminate the surface of the wafer at a predetermined location and angle within a selected exposure field 14 '(shaded in dark color). The position can already be found with sufficient accuracy by the first measuring step. A sensor can be used to detect the beam reflected by the surface, from which it is possible to calculate the tilt angle of the surface, ie the tilt of the wafer. The wafer stage can be adjusted according to the result.

  Eight exposure fields 14 'are provided for this alignment measurement step. These exposure fields are further arranged each at a distance not far from the edge of the wafer 10, so this circular arrangement of choices can further define a single warp (with different exposure field tilts). angle).

  The alignment optical element here is a sensor arrangement for tilt measurement, i.e. measurement of the local angle of tilt in the exposure field. Here, the wafer stage moves each of the exposure fields toward the tilt sensor, which can then perform a tilt measurement. In order to minimize the travel path, and thus to save time for this alignment step, the wafer stage scans a circularly selected portion in a circular fashion clockwise. The sequence of exposure fields for the measurement step (as is the case with all other drawings) is represented by the numbers 14, 14 ', etc. in the selected exposure field.

  The first exposure field to be measured is arbitrarily placed at the lower right in the array. Therefore, the wafer stage begins with the GTILT measurement (FIG. 1B: No. 1 in the sequence) from the exposure field 14 measured at the end of the TVPA measurement (FIG. 1A: No. 2 in the sequence, position in the matrix array: row 5, column 7). Position in the matrix array: row 2, column 6) moved through the distance to the first exposure field 14 'to be measured. This corresponds to a distance of about 100 mm.

  In the following, as a further alignment measurement step, only one exposure field is used to control the lens (LCVC, lens control value check: FIG. 1C) and the reference value (SPOC, sensor) of the distance between the sensor and the alignment mark. Pattern offset check: a check for deviation from FIG. 1D) is carried out, for which again a larger number of selected exposure fields 14 ″ are required. In this case as well, the process starts with the wafer 10 located in the lower right and in the exposure field representing an arbitrary start position.

  1E and 1F show fine alignment steps (advanced global alignment, AGA_prel and AGA_main), and the configuration shown in FIG. 1E represents pre-alignment performed separately. In this case, the field marked with an asterisk identifies the position of the field additionally used in the main alignment (FIG. 1F). In these measurement steps, the wafer stage is accurately fitted with a few nanometers in the XY image plane for subsequent exposure. Here, the alignment marks in the exposure field have the shape of parallel square bars extending long in the X or Y direction. In this case, a deviation from a reference position (for example, a reference mark) is measured by an alignment optical element having a lens system. The alignment optical element here comprises a high resolution lens system.

  The measurement sequence in the matrix array is subject to any condition that it starts at the bottom or right at the bottom, and a comparison between FIG. 1E and FIG. 1F again shows that the wafer stage is row 2, column 3 ) To row 2, column 6 (# 1 in FIG. 1F), indicating that this then represents a long travel path.

  Exposure (compared to FIG. 1G) is performed over all fields of the matrix arrangement shown, i.e. all exposure fields 12 also cover the edge area. Based on any considerations to generate a uniform movement schema for the wafer stage, the exposure sequence further starts at the lower right in the matrix array, ie, position row 8, column 6, and again fine alignment. Is different from the last measured position row 7 and column 3. Therefore, the wafer stage must be moved at the start of exposure.

  The method according to the invention is shown in FIG. The alignment measurement step in FIGS. 2A to 2G corresponds to the above-described measurement step in FIGS. 1A to 1G. With the present invention, differences occur due to the invention in the selection and sequence of exposure fields.

  Thus, for example, the exposure field 16 ′ (No. 1) initially used for the measurement in the alignment step of the GTILT measurement (FIG. 2B) is the last field measured in the sequence of the TVPA measurement (FIG. 2A) (in the selection It has the same position (row 6, column 6) as No. 2 of the two exposure fields. Thus, the wafer stage is advantageously not moved during the transition from the first to the second alignment measurement step.

  For example, the same is true if the second or later wafer 10 'in the batch (indicated by the arrow in FIG. 2) is to be aligned. In this case, fine alignment (FIG. 1E) starts immediately after TVPA measurement (FIG. 1A). The first exposure field takes this position as well.

  Therefore, according to the present invention, the selection of the exposure process depends on the exposure process of the previous process. This is because the last exposure field of the previous alignment measurement step must at least be covered by selection. Furthermore, the current sequence of alignment measurement steps depends on the sequence of previous alignment measurement steps.

  In the case of an alignment measurement step including one selected exposure field 16 of the lens control (FIG. 2C), the position of one selected exposure field is further adapted to this condition. Since the pre-measurement (# 8 in FIG. 2b) is located near the edge area of the wafer, the position of the exposure field to be measured here (# 1 in FIG. 2C) is also near the edge area, and It is the same as the position (No. 8) of the exposure field measured last.

  For the SPOC measurement (FIG. 2D), again, no moving movement of the wafer stage is necessary. From the end of tilt measurement (FIG. 2B) to the start of SPOC measurement (FIG. 2D), no moving motion is performed. Here, the contribution rate of the saved time is particularly high in terms of distribution.

  2E and 2F, the method according to the present invention regarding the selection and sequence of exposure fields is consistently maintained for fine alignment of the first wafer in a batch.

  The exposure (FIG. 2G) is also adapted to the new state by the method according to the invention. This is because the exposure field partially protruding on the edge of the wafer can hardly be used for alignment, so the first exposure field (number 1 in FIG. 2G) is the last measurement in the case of fine alignment. It is drawn into the matrix arrangement of the corresponding position (6: row 7, column 5) and adapted to the sequence of the remaining 55 exposure fields.

  For each step in which the measurement is performed in a sequence of measurement steps for aligning the wafer in the exposure apparatus, the last used exposure field on the semiconductor wafer is the first exposure field of the measurement associated with the new alignment step, Used for the alignment step that immediately follows in the sequence. That is, in a subsequent step, this exposure field is moved as the first exposure field before the appropriate alignment optics for measurement. As a result, movement of the movable wafer stage is avoided at each step, thereby saving valuable equipment time for exposing the semiconductor product.

  As mentioned above, although this invention has been illustrated using preferable embodiment of this invention, this invention should not be limited and limited to this embodiment. It is understood that the scope of the present invention should be construed only by the claims. It is understood that those skilled in the art can implement an equivalent range based on the description of the present invention and the common general technical knowledge from the description of specific preferred embodiments of the present invention. Patents, patent applications, and documents cited herein should be incorporated by reference in their entirety, as if the contents themselves were specifically described herein. Understood.

FIG. 1A shows a sequence of alignment measurement steps for selecting an exposure field to be used for measurement, and a sequence of measurements according to an exemplary method according to the prior art. FIG. 1B shows a sequence of alignment measurement steps for selecting an exposure field to be used for measurement, and a sequence of measurements according to an exemplary method according to the prior art. FIG. 1C shows a sequence of alignment measurement steps for selecting an exposure field to be used for measurement, and a sequence of measurements according to an exemplary method according to the prior art. FIG. 1D shows a sequence of alignment measurement steps for selecting an exposure field to be used for measurement and a measurement sequence according to an exemplary method according to the prior art. FIG. 1 shows a sequence of alignment measurement steps for selecting an exposure field to be used for measurement and a measurement sequence according to an exemplary method according to the prior art. FIG. 1F shows a sequence of alignment measurement steps for selecting an exposure field to be used for measurement, and a sequence of measurements by an exemplary method according to the prior art. FIG. 1G shows a sequence of alignment measurement steps for selecting an exposure field to be used for measurement, and a sequence of measurements according to an exemplary method according to the prior art. FIG. 2A is similar to FIG. 1, but in accordance with an exemplary method according to the present invention. FIG. 2B is a view similar to FIG. 1, but according to an exemplary method in accordance with the present invention. FIG. 2C is similar to FIG. 1 but according to an exemplary method according to the present invention. FIG. 2D is a view similar to FIG. 1 but according to an exemplary method in accordance with the present invention. FIG. 2E is similar to FIG. 1, but in accordance with an exemplary method according to the present invention. FIG. 2F is similar to FIG. 1 but in accordance with an exemplary method according to the present invention. FIG. 2G is similar to FIG. 1, but in accordance with an exemplary method according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor wafer 12 Exposure field 14 of matrix shape arrangement | sequence on wafer Selected exposure field (prior art)
14 'Selected exposure field (prior art)
14 '' selected exposure field (prior art)
16 Selected exposure field (according to the invention)
16 'selected exposure field (according to the invention)

Claims (5)

A method for controlling a sequence of measurement steps for aligning a semiconductor wafer (10) in an exposure apparatus, the semiconductor wafer having a regular array of exposure fields (12), the method comprising:
a) preparing the semiconductor wafer (10) in the exposure apparatus;
b) starting a first alignment measurement step;
c) selecting the first number of exposure fields (16) and determining the first sequence (No. 1, No. 2), in each case for performing at least one measurement The number of the selected exposure fields (16) is used, and
d) Using a movable wafer stage to move each of the selected exposure fields (16, 1, 2), the semiconductor wafer (10) relative to the alignment optics of the exposure apparatus Moving to an alignment position;
e) storing the alignment position of the last moved exposure field (16, 2);
f1) ending the first alignment measurement step;
f2) starting a second alignment measurement step that immediately follows;
g) selecting the exposure field (16 ′, number 1) where the position is stored in order to perform the first measurement in the second sequence of exposure fields in the exposure field;
h) selecting an additional number of exposure fields (16 ′) and determining the second sequence (No. 2 to No. 8), after the first measurement in the sequence, respectively The number of the further selected exposure fields (16 ′, # 2-8) is utilized to perform at least one further measurement;
i) For the alignment measurement step that immediately follows, the steps d) to f1) are repeated.   Said first and / or said second alignment measuring steps each determine a first coarse alignment of said wafer in an image plane of said exposure apparatus, an inclination of said wafer (10) relative to said image plane; The method according to claim 1, characterized in that it comprises the elements of the group consisting of fine alignment of the wafer (10) in the image plane.   The method according to claim 2, characterized in that the steps d) to f1) are repeated for all alignment measurement steps before the exposure of the semiconductor wafer (10). A method of sequentially exposing wafers each having a mask structure pattern in an exposure apparatus after completing a plurality of alignment steps, the wafer (10) having a regular array of exposure fields (12) Because
An exposure field (No. 12, No. 1) to be exposed first on the wafer in the exposure sequence (No. 1 to No. 56) is used to perform measurement in an alignment measurement step executed immediately before the exposure step. And the same exposure field (16) used as the last exposure field (16, 6).   The method according to claim 4, wherein the alignment step performed immediately before the exposure step is a fine alignment step of the semiconductor wafer in an image plane of the exposure apparatus.

Images